I'm in Alaska down in Soldotna.
My coop was made from sandwich panels we made.
Plywood and 2x2's with inch and a half R-Tec in between.
It's pretty well insulated.
I did add a few circular vents though.
You would likely need supplemental heat at -50*.
I would consider a milkhouse style heater if you have power.
Set it for roughly 35* or so.
Not sure how a greenhouse coop would work in the Alaska winter? The lack of daylight might negate any benefits?